Photographic process printers use a cathode ray tube (CRT) to project an image onto a photosensitive media. After the image is projected onto the media, the media is processed to develop the latent image. In order to transfer the image from the surface of the CRT to the surface of the media while maintaining image focus, prior art devices typically use lenses or an array of optical fibers that are adapted to transfer the light from the surface of the CRT to the surface of the media.
A problem exists when applying this technology to create wide format images on wide format photosensitive media. Large CRTs are inherently complex in their design due to factors relating to the wide ranging sweep of the electron beam within the CRT and the difficulty of manufacturing a large glass envelope. Alternatively, lenses are required to magnify the image of the CRT face, resulting in reduced resolution and increased exposure time. Retaining the quality required for the print process of photographic printer devices requires large CRTs representing significant cost and complexity in the resulting photographic printer device. A practical limit on the CRT width in these applications is less than the width desired for wide format photosensitive media.
One option is to divide the image onto a plurality of smaller CRTs. This option presents problems in that CRTs cannot be physically mounted horizontally or vertically adjacent one another so as to create a seamless image row. All known CRT devices are manufactured with some non-imageable area at their sweep limits. Additionally, physical thickness of the CRT glass envelope material will preclude precise, seamless alignment of the plurality of partial images on the CRTs.
Although optical fibers are one technique used to transfer the image from the projection surface of each CRT onto the surface of the photosensitive media, these fibers must remain short enough to prevent excessive loss of image light intensity. The short length of the optical fibers, and the cost of longer fiber arrays, preclude physical recomposition of the whole image by simply bending the optical fibers so that the fibers at the ends of adjacent partial image segments are abutted.
One prior art system is shown in U.S. Pat. No. 5,373,347 issued Dec. 13, 1994 to Shaklee, et al., entitled "Staggered Multiple CRTs in a Photographic Process Printer", which is incorporated herein by reference for all that is disclosed and taught therein. This system has a limitation in that the print media must be kept very straight as it moves across the staggered CRTs. Any buckling or wobbling of the print paper causes distortion in the output image.
Another limitation of this system is the requirement for precise paper movement, so that the dot rows of vertically spaced CRTs can be aligned on the same dot row of the media.
It is thus apparent that there is a need in the art for an improved method or apparatus which permits efficient transfer of a wide format image onto photosensitive media from a plurality of CRTs. The present invention meets this and other needs in the art.